Fuel control device, combustion chamber, gas turbine, fuel control method and program

Abstract

A fuel control device (10) for a gas turbine (1), which gas turbine (1) comprises: a combustion chamber (60) for burning a fuel gas supplied from a first fuel nozzle (601), a second fuel nozzle (602) and a third fuel nozzle (603), of which the second fuel nozzle (602) contributes the most to the combustion in the combustion chamber (60) to produce a high-temperature combustion gas, a main fuel supply line (Ra) in which a first flow rate adjusting valve (20) is arranged and from which a first branch line (R1), a second branch line (R2) and a third branch line (R3) branch off, wherein the first branch line (R1) is connected to the first fuel nozzle (601) and whose flow rate is controlled by a second flow rate adjusting valve (30), the second branch line (R2) is connected to the second fuel nozzle (602) and whose flow rate is controlled by a third flow rate adjustment valve (40), and the third branch line (R3) is connected to the third fuel nozzle (603) and whose flow rate is controlled by a fourth flow rate adjustment valve (50), wherein the fuel control device (10) comprises: a trunk / main fuel valve opening degree determining unit (101) configured to determine an opening degree of the first flow rate adjusting valve (20) of the trunk / main fuel supply line (Ra) on the basis of a fuel control signal command value corresponding to a power of the gas turbine (1), a branch line flow rate determination unit (102) configured to determine the degree of opening of each of the second, third, and fourth flow rate adjustment valves (30, 40, 50) of the first, second, and third branch lines (R1, R2, R3) and thus the respective fuel distribution ratios of the first fuel nozzle (601), the second fuel nozzle (602), and the third fuel nozzle (603) on the basis of an operating situation of the gas turbine (1), and a correction value determination unit (103) configured to determine a correction value of the opening degree of each of the second, third, and fourth flow rate adjusting valves (30, 40, 50) of the first, second, and third branch lines (R1, R2, R3) based on a value of a pressure difference between a fuel pressure upstream of each of the first, second, and third fuel nozzles (601, 602, 603) and a corrected fuel pressure for the fuel pressure at an outlet of the first, second, and third fuel nozzles (601, 602, 603), wherein the correction value determining unit (103) is configured to determine the correction value for the fourth flow rate adjusting valve (50) in order to reduce the fuel distribution ratio of the third fuel nozzle (603) in a case where the pressure difference between the fuel pressure upstream of the second fuel nozzle (602) and the corrected fuel pressure for the fuel pressure at the outlet of the second fuel nozzle (602) is reduced.

Description

[0001] The present invention relates to a fuel control device, a combustor, a gas turbine, a fuel control method and a program.

[0002] Priority is claimed to Japanese patent application No. 2016-044242, filed on March 8, 2016.

[0003] There is a gas turbine that has a combustion chamber that has a multitude of nozzles.

[0004] As a related technology, JP 2007-77866 A discloses a technology that includes a combustor having a plurality of nozzles and controls a fuel flow rate based on an operating state of a gas turbine.

[0005] JP H11-343869 A shows that a diffusion pilot burner is located in the center of the upstream end of a gas turbine combustion chamber. Annular premix burners with a plurality of fuel nozzles and flame stabilizers for the premix burner are arranged on the outer periphery. In this case, fuel systems for the diffusion pilot burner and fuel systems for the premixed burner are provided, branching off from a main fuel system 200. In a low load range, operation is carried out by a diffusion pilot burner. In a certain load range, the fuel flow to the diffusion pilot burner is reduced, the fuel flow of the premixed burner fuel system is increased, and the fuel flow of the diffusion pilot burner fuel system is set to zero.

[0006] JP 2016-23594 A discloses a fuel flow controller comprising: a flow estimation unit that detects pressures upstream and downstream of a nozzle provided downstream of a fuel flow control valve from a state variable of fuel flowing in a fuel system in which the fuel flow control valve is provided, and estimates a flow amount of the fuel flowing in the nozzle based on the detected pressures; and a valve opening degree setting unit that sets an opening degree of the fuel flow control valve based on an estimation result of the flow estimation unit.

[0007] JP H05-149544 A discloses a first main nozzle function generator that outputs a first main nozzle control signal to a tracking circuit based on a load speed control signal, and a second main nozzle function generator that outputs a second main nozzle control signal to the tracking circuit based on the exhaust port temperature of a burner. The tracking circuit outputs a third main nozzle control signal, in which the second main nozzle control signal follows the first main nozzle control signal, to a main nozzle distribution valve. A pilot nozzle function generator inputs the third main nozzle control signal and actuates a pilot nozzle distribution valve. According to this method, the flame is stabilized even during a sudden change in the fuel flow rate, and the peak number of revolutions can be reduced.

[0008] Furthermore, there may be a problem that when pressure differences between a fuel pressure upstream of each of the nozzles of a combustion chamber and a corrected fuel pressure for the fuel pressure at an outlet change, the combustion characteristics of the gas turbine change.

[0009] Therefore, it is an object of the present invention to provide a fuel control device, a combustor, a gas turbine, a fuel control method and a program capable of solving the above problem.

[0010] The object is achieved by a fuel control device according to claim 1, a gas turbine according to claim 5, a fuel control method for a gas turbine according to claim 6 and by a program according to claim 7. The dependent claims relate to further advantageous embodiments of the invention.

[0011] According to the fuel control device according to the embodiment of the present invention, it is possible to prevent a fluctuation in combustion characteristics of a gas turbine that occurs in a case where a pressure difference between a fuel pressure upstream of each of the nozzles of a combustor and a corrected fuel pressure for the fuel pressure at an outlet changes. Fig. 1 is a diagram showing a configuration of a gas turbine according to an embodiment of the present invention. Fig. 2 is a diagram showing a relationship between a fuel control signal command value and a third fuel distribution ratio in an embodiment of the present invention. Fig. 3 is a diagram showing a relationship between the fuel control signal command value and a Δthird fuel distribution ratio in an embodiment of the present invention. Fig. 4 is a diagram showing a relationship between a pressure difference of a second fuel nozzle and a correction coefficient according to an embodiment of the present invention. Fig. 5 is a diagram showing a relationship between the pressure difference of a second fuel nozzle and combustion characteristics of the gas turbine according to an embodiment of the present invention. Fig. 6 is a diagram showing a relationship between a first fuel distribution ratio and a pressure difference of a first fuel nozzle and a relationship between the first fuel distribution ratio and fuel properties, respectively, according to an embodiment of the present invention.

[0012] An embodiment will be described in detail below with reference to the drawings.

[0013] A structure of a gas turbine 1 according to an embodiment of the present invention will be described.

[0014] As shown in Fig. 1, the gas turbine 1 according to an embodiment of the present invention includes a fuel control device 10, a first flow rate adjusting valve 20, a second flow rate adjusting valve 30, a third flow rate adjusting valve 40, a fourth flow rate adjusting valve 50, a combustion chamber 60, and a turbine body 70.

[0015] In addition, Fig. 1, a trunk / main fuel supply line is designated by a reference symbol Ra. In addition, Fig. 1, a first branch line, which is one of a plurality of branch lines branching off from the trunk / main fuel supply line Ra, is designated by reference symbol R1. In addition, in Fig. 1 a second branch line branching off from the trunk / main fuel supply line Ra is designated by reference symbol R2 and a third branch line branching off from the trunk / main fuel supply line Ra is designated by reference symbol R3.

[0016] The fuel control device 10 includes a trunk / main fuel valve opening degree determining unit 101, a branch line flow rate determining unit 102, and a correction value determining unit 103.

[0017] The trunk / main fuel valve opening degree determining unit 101 determines an opening degree of a flow rate adjusting valve (the first flow rate adjusting valve 20) of the trunk / main fuel supply line Ra serving as the base of a plurality of branch lines (the first branch line R1, the second branch line R2, and the third branch line R3) based on a fuel control signal command value according to an output of the gas turbine 1. For example, the fuel control signal command value corresponding to the output of the gas turbine 1 is defined as a value proportional to an output of an electric generator (not shown) driven by the gas turbine 1 or as a value proportional to a gas turbine inlet fuel gas temperature.

[0018] The branch line flow rate determining unit 102 determines the opening degrees of each of the flow rate adjusting valves (the second flow rate adjusting valve 30, the third flow rate adjusting valve 40, and the fourth flow rate adjusting valve 50) of the plurality of branch lines branching from the trunk / main fuel supply line Ra based on an operation situation of the gas turbine 1.

[0019] The correction value determining unit 103 determines a correction value of the opening degree of each flow rate adjusting valve of the branch line based on a value of a pressure difference (described as a “nozzle pressure difference” in the drawing) between a fuel pressure upstream of each of the nozzles (a first fuel nozzle 601, a second fuel nozzle 602, and a third fuel nozzle 603, which will be described later) respectively connected to the branch lines and a corrected fuel pressure for the fuel pressure at an outlet.

[0020] The first flow rate adjusting valve 20 adjusts a flow rate of the trunk / main fuel supply line Ra based on control by the trunk / main fuel valve opening degree determining unit 101.

[0021] The second flow rate adjusting valve 30 adjusts a flow rate to the first branch line R1 from the trunk / main fuel supply line Ra based on control by the branch line flow rate determining unit 102.

[0022] The third flow rate adjusting valve 40 adjusts a flow rate to the second branch line R2 from the trunk / main fuel supply line Ra based on control by the branch line flow rate determining unit 102.

[0023] The fourth flow rate adjusting valve 50 adjusts a flow rate to the third branch line R3 from the trunk / main fuel supply line Ra based on control by the branch line flow rate determining unit 102.

[0024] The combustion chamber 60 includes the first fuel nozzle 601, the second fuel nozzle 602 and the third fuel nozzle 603.

[0025] The first fuel nozzle 601 is connected to the first branch line R1.

[0026] The second fuel nozzle 602 is connected to the second branch line R2.

[0027] The third fuel nozzle 603 is connected to the third branch line R3.

[0028] The combustion chamber 60 combusts a fuel gas supplied from each of the first fuel nozzle 601, the second fuel nozzle 602, and the third fuel nozzle 603 to generate a high-temperature combustion gas. The combustion chamber 60 discharges the generated high-temperature combustion gas to the turbine body 70.

[0029] The turbine body 70 converts thermal energy obtained by expanding the high-temperature combustion gas and supplied from the combustion chamber 60 into rotational energy of a rotor (a rotor shaft).

[0030] The gas turbine 1 according to an embodiment of the present invention determines the opening degree of the flow rate adjusting valve of the trunk / main fuel supply line Ra based on the fuel control signal command value according to a performance of the gas turbine 1 and determines the flow rate of the trunk / main fuel supply line Ra. The gas turbine 1 determines the opening degrees of each of the flow rate adjusting valves of the plurality of branch lines branching from the trunk / main fuel supply line Ra based on the operating situation of the gas turbine 1. A distribution of the flow rates supplied to each of the plurality of branch lines from the trunk / main fuel supply line Ra is determined by determining the opening degrees.The gas turbine 1 determines the correction value of the opening degrees of each of the flow rate adjusting valves of the branch line based on the value of the pressure difference between the fuel pressure upstream of each of the nozzles connected to the branch lines respectively and the corrected fuel pressure for the fuel pressure at the outlet, and corrects the fuel pressure of the flow rates supplied to each of the plurality of branch lines from the trunk / main fuel supply line Ra.

[0031] Therefore, the gas turbine 1 can prevent fluctuations in combustion characteristics of the gas turbine 1 due to fluctuations in the pressure difference between the fuel pressure upstream of each of the nozzles connected to the branch lines respectively and the corrected fuel pressure for the fuel pressure at the outlet by determining the correction value of the opening degrees of each of the flow rate adjusting valves of the branch line based on the value of the pressure difference between the fuel pressure upstream of each of the nozzles connected to the branch lines respectively and the corrected fuel pressure for the fuel pressure at the outlet and correcting the distribution of the flow rates supplied to each of the plurality of branch lines from the trunk / main fuel supply line Ra.

[0032] First, an example will be described in which a fluctuation of combustion characteristics of the gas turbine 1 due to a fluctuation of a pressure difference between a fuel pressure upstream of the second fuel nozzle 602, which contributes most to combustion in the combustor 60, and the corrected fuel pressure for the fuel pressure at an outlet is avoided.

[0033] The pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet can be obtained by the following formula (1). The pressure difference of the second nozzle 602 = a collector pressure − a pressure of the combustion chamber 60

[0034] It is noted that the manifold pressure of the second fuel nozzle 602 is determined using a pressure gauge.

[0035] A casing pressure is determined using a pressure gauge, and the pressure of the combustion chamber 60 (a pressure upstream of the turbine body 70) can be obtained by calculating (cabin pressure) × α.

[0036] A relationship between the fuel control signal command value and a Δ third fuel distribution ratio corresponding to the power of the gas turbine 1 shown in Fig. 3 can be obtained by converting the third fuel distribution ratio into a relationship between the fuel control signal command value and a third fuel distribution ratio corresponding to the power of the gas turbine 1 shown in Fig. 2, from 0 to 1.

[0037] In an example of a relationship between the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet and a correction coefficient shown in Fig. 4, the correction coefficient is 0 in a case where the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet is greater than Pr1 [MPa] (megapascals). Furthermore, in an example of the relationship between the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet and the correction coefficient shown in Fig. 4, the correction coefficient decreases as the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet decreases from Pr1 [MPa].

[0038] The relationship between the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet and the correction coefficient can be determined as follows. This means that a relationship between the second fuel nozzle 602 in the gas turbine 1 and the combustion characteristics of the gas turbine 1 as shown in Fig. 5, and in a case where the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet is equal to or smaller than Pr1 [MPa], for example, the gas turbine 1 determines a correction for reducing the third fuel distribution ratio and executes this correction.The pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet increases, and it is possible to reduce a fluctuation in the combustion characteristics of the gas turbine 1 by performing the correction to reduce the third fuel distribution ratio in a case where the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet is equal to or less than Pr1 [MPa].

[0039] It should be noted that the relationship between the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet and the correction coefficient can be determined by conducting an experiment on the actual gas turbine 1 and on the basis of experiment results therefrom.

[0040] In addition, with respect to the example of the relationship between the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet and the combustion characteristics of the gas turbine 1 shown in Fig. 5, it is determined to perform a correction that reduces the third fuel distribution ratio in a case where the pressure difference is equal to or less than Pr1 [MPa], but the present invention is not limited to this. A range of the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet when the correction is determined to reduce the third fuel distribution ratio is approximately 0.1 [MPa] to 1 [MPa].

[0041] The correction value of the third fuel distribution ratio can be obtained by multiplying the third fuel distribution ratio shown in Fig. 3, with the correction coefficient shown in Fig. 4, can be obtained.

[0042] This means that a third fuel distribution ratio FTH after correction can be calculated by the following formula (2) using a third fuel distribution ratio FX1 before correction shown in Fig. 2, of the third fuel distribution ratio shown in Fig. 3, and the correction coefficient shown in Fig. 4. FTH=FX1+FX2×FX3

[0043] The trunk / main fuel valve opening degree determining unit 101 determines the opening degree of the flow rate adjusting valve (the first flow rate adjusting valve 20) of the trunk / main fuel supply line Ra based on the fuel control signal command value according to the performance of the gas turbine 1. The branch line flow rate determining unit 102 determines the opening degrees of each of the flow rate adjusting valves (the second flow rate adjusting valve 30, the third flow rate adjusting valve 40, and the fourth flow rate adjusting valve 50) of the plurality of branch lines (the first branch line R1, the second branch line R2, and the third branch line R3) branching from the trunk / main fuel supply line Ra based on the operating situation of the gas turbine 1.In a case where the fluctuation in the combustion characteristics of the gas turbine 1 is prevented due to a reduction in the pressure difference between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet, the correction value determining unit 103 increases the ratio of the third fuel control signal command value and increases the second fuel control signal command value based on the pressure difference value between the fuel pressure upstream of the second fuel nozzle 602 and the corrected fuel pressure for the fuel pressure at the outlet.

[0044] Next, an example will be described in which a fluctuation in the combustion characteristics of the gas turbine 1 due to a fluctuation in a pressure difference between a fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at an outlet in the combustor 60 is prevented.

[0045] Incidentally, in a case where the fluctuation in the combustion characteristics of the gas turbine 1 due to the fluctuation in the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 of the combustor 60 and the corrected fuel pressure for the fuel pressure at the outlet is prevented, a first fuel control signal command value is controlled based on the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet.

[0046] For example, if a relationship between the first fuel distribution ratio and the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet or a relationship between the first fuel distribution ratio and fuel properties shown in Fig. 6 in a case where the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet is equal to or less than Pr2 [MPa], it is determined from the relationship between the first fuel distribution ratio and the fuel properties to make a correction that increases the first fuel distribution ratio.The pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet increases, and it is possible to prevent the fluctuation in the combustion characteristics of the gas turbine 1 by performing the correction that increases the first fuel distribution ratio in a case where the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet is equal to or less than Pr2 [MPa].

[0047] It should be noted that the relationship between the first fuel distribution ratio and the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet can be determined by conducting an experiment on the actual gas turbine 1 and based on an experiment result therefrom.

[0048] Furthermore, with reference to the example of the relationship between the first fuel distribution ratio and the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet shown in Fig.6, it is determined to perform the correction that increases the first fuel distribution ratio in a case where the pressure difference is equal to or less than Pr2 [MPa], but the present invention is not limited to this. The range of the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet, which is determined to perform the correction that increases the first fuel distribution ratio, is approximately 0.01 [MPa] to 0.1 [MPa].

[0049] The trunk / main fuel valve opening degree determining unit 101 determines the opening degree of the flow rate adjusting valve (the first flow rate adjusting valve 20) of the trunk / main fuel supply line Ra based on the fuel control signal command value according to the performance of the gas turbine 1. The branch line flow rate determining unit 102 determines the opening degrees of each flow rate adjusting valve (the second flow rate adjusting valve 30, the third flow rate adjusting valve 40, and the fourth flow rate adjusting valve 50) of the plurality of branches branching from the trunk / main fuel supply lines (the first branch line R1, the second branch line R2, and the third branch line R3) based on the operating situation of the gas turbine 1.In a case where the fluctuation in the combustion characteristics of the gas turbine 1 is avoided due to the reduction of the pressure difference between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet, the correction value determining unit 103 increases the ratio of the first fuel control signal command value based on the pressure difference value between the fuel pressure upstream of the first fuel nozzle 601 and the corrected fuel pressure for the fuel pressure at the outlet.

[0050] The gas turbine 1 according to an embodiment of the present invention has been described above. In the gas turbine 1, the fuel control device 10 includes the parent / main fuel valve opening degree determination unit 101, the branch line flow rate determination unit 102, and the correction value determination unit 103. The parent / main fuel valve opening degree determination unit 101 determines the opening degree of the flow rate adjustment valve (the first flow rate adjustment valve 20) of the parent / main fuel supply line Ra based on the fuel control signal command value according to the power of the gas turbine 1.The branch line flow rate determining unit 102 determines the opening degrees of each of the flow rate adjusting valves (the second flow rate adjusting valve 30, the third flow rate adjusting valve 40, and the fourth flow rate adjusting valve 50) of the plurality of branch lines (the first branch line R1, the second branch line R2, and the third branch line R3) branching from the trunk / main fuel supply line Ra, based on the operating situation of the gas turbine 1. The correction value determining unit 103 determines the correction value of the opening degree of each flow rate adjusting valve of the branch line based on the value of a pressure difference between the fuel pressure upstream of each of the nozzles (the first fuel nozzle 601, the second fuel nozzle 602, and the third fuel nozzle 603) connected to the branch lines, respectively, and the corrected fuel pressure for the fuel pressure at the outlet.

[0051] Therefore, the fuel control device 10 can prevent the fluctuation in the combustion characteristics of the gas turbine 1 that occurred in a case where the pressure difference between the fuel pressure upstream of each of the nozzles of the combustor 60 and the corrected fuel pressure for the fuel pressure at the outlet varies.

[0052] Although the embodiment of the present invention has been described, the above-described fuel control device 10 may include a computer system. Furthermore, procedures for the above-described methods may be stored in a computer-readable recording medium in the form of a program, and the above-described methods may be performed by the computer reading and executing the program. Here, the computer-readable recording media may include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, and the like. Furthermore, the computer program may be distributed to the computer through a communication line, and the computer receiving the distribution may execute the program.

[0053] Furthermore, the program described above can realize some of the functions described above. Furthermore, the program described above can be a file capable of realizing the functions described above by combining it with a program pre-stored in the computer system, a so-called difference file (a difference program).

[0054] Although various embodiments of the present invention have been described, these embodiments are examples and do not limit the scope of the invention. Various additions, omissions, substitutions, and changes may be made to these embodiments without departing from the spirit of the invention.

[0055] According to the fuel control device according to the embodiment of the present invention, it is possible to prevent fluctuations in combustion characteristics of a gas turbine that occur in a case where a pressure difference between a fuel pressure upstream of each of the nozzles of a combustor and a corrected fuel pressure for the fuel pressure at an outlet varies. List of reference symbols 1 gas turbine 10 Fuel control device 20 First flow rate adjustment valve 30 Second flow rate adjustment valve 40 Third flow rate adjustment valve 50 Fourth flow rate adjustment valve 60 combustion chamber 70 turbine bodies 101 Trunk / main fuel valve opening degree determination unit 102 Branch line flow rate determination unit 103 Correction value determination unit 601 First fuel nozzle 602 Second fuel nozzle 603 Third fuel nozzle

Claims

[1] A fuel control device (10) for a gas turbine (1), which gas turbine (1) comprises: a combustion chamber (60) for burning a fuel gas supplied from a first fuel nozzle (601), a second fuel nozzle (602) and a third fuel nozzle (603), of which the second fuel nozzle (602) contributes the most to the combustion in the combustion chamber (60) to produce a high-temperature combustion gas, a main fuel supply line (Ra) in which a first flow rate adjusting valve (20) is arranged and from which a first branch line (R1), a second branch line (R2) and a third branch line (R3) branch off, wherein the first branch line (R1) is connected to the first fuel nozzle (601) and whose flow rate is controlled by a second flow rate adjusting valve (30), the second branch line (R2) is connected to the second fuel nozzle (602) and whose flow rate is controlled by a third flow rate adjustment valve (40), and the third branch line (R3) is connected to the third fuel nozzle (603) and whose flow rate is controlled by a fourth flow rate adjustment valve (50), wherein the fuel control device (10) comprises: a trunk / main fuel valve opening degree determining unit (101) configured to determine an opening degree of the first flow rate adjusting valve (20) of the trunk / main fuel supply line (Ra) on the basis of a fuel control signal command value corresponding to a power of the gas turbine (1), a branch line flow rate determination unit (102) configured to determine the opening degree of each of the second, third, and fourth flow rate adjustment valves (30, 40, 50) of the first, second, and third branch lines (R1, R2, R3) and thus the respective fuel distribution ratios of the first fuel nozzle (601), the second fuel nozzle (602), and the third fuel nozzle (603) on the basis of an operating situation of the gas turbine (1), and a correction value determination unit (103) configured to determine a correction value of the opening degree of each of the second, third, and fourth flow rate adjusting valves (30, 40, 50) of the first, second, and third branch lines (R1, R2, R3) based on a value of a pressure difference between a fuel pressure upstream of each of the first, second, and third fuel nozzles (601, 602, 603) and a corrected fuel pressure for the fuel pressure at an outlet of the first, second, and third fuel nozzles (601, 602, 603), wherein the correction value determining unit (103) is configured to determine the correction value for the fourth flow rate adjusting valve (50) in order to reduce the fuel distribution ratio of the third fuel nozzle (603) in a case where the pressure difference between the fuel pressure upstream of the second fuel nozzle (602) and the corrected fuel pressure for the fuel pressure at the outlet of the second fuel nozzle (602) is reduced. [2] The fuel control device (10) according to claim 1, wherein the correction value determining unit (103) is arranged to determine the correction value of the opening degree of each of the second, third and fourth flow rate adjusting valves (30, 40, 50) of the first, second and third branch lines (R1, R2, R3) in the case where the pressure difference between the fuel pressure upstream of the second fuel nozzle (602) and the corrected fuel pressure for the fuel pressure at the outlet of the second fuel nozzle (602) is in a range of 0.1 megapascal to 1 megapascal. [3] The fuel control device (10) according to claim 1 or 2, wherein the correction value determining unit (103) is configured to, in a case where the pressure difference between the fuel pressure upstream of the first fuel nozzle (601) and the corrected fuel pressure for the fuel pressure at an outlet of the first fuel nozzle (601) is reduced, determine the correction value for the second flow rate adjusting valve (30) to reduce the fuel distribution ratio of the first fuel nozzle (601). [4] The fuel control device (10) according to any one of claims 1 to 3, wherein the correction value determining unit (103) is configured to determine the correction value for the opening degree of each of the second, third and fourth flow rate adjusting valves (30, 40, 50) of the first, second and third branch lines (R1, R2, R3) in a case where the pressure difference between the fuel pressure upstream of the first fuel nozzle (601) and the corrected fuel pressure for the fuel pressure at the outlet of the first fuel nozzle (601) is in a range of 0.01 megapascals to 0.1 megapascals. [5] A gas turbine (1) comprising: a combustion chamber (60) having a first fuel nozzle (601), a second fuel nozzle (602) and a third fuel nozzle (603), from which fuel gas is supplied for combustion to produce a high-temperature combustion gas, and of which the second fuel nozzle (602) contributes most to combustion in the combustion chamber (60), a main fuel supply line (Ra) in which a first flow rate adjusting valve (20) is arranged and from which a first branch line (R1), a second branch line (R2) and a third branch line (R3) branch off, wherein the first branch line (R1) is connected to the first fuel nozzle (601) and whose flow rate is controlled by a second flow rate adjusting valve (30), the second branch line (R2) is connected to the second fuel nozzle (602) and whose flow rate is controlled by a third flow rate adjustment valve (40), and the third branch line (R3) is connected to the third fuel nozzle (603) and whose flow rate is controlled by a fourth flow rate adjusting valve (50), and the fuel control device (10) according to any one of claims 1 to 4. [6] A fuel control method for a gas turbine (1), which gas turbine (1) comprises: a combustion chamber (60) for burning a fuel gas supplied from a first fuel nozzle (601), a second fuel nozzle (602) and a third fuel nozzle (603), of which the second fuel nozzle (602) contributes the most to the combustion in the combustion chamber (60) to produce a high-temperature combustion gas, a main fuel supply line (Ra) in which a first flow rate adjusting valve (20) is arranged and from which a first branch line (R1), a second branch line (R2) and a third branch line (R3) branch off, wherein the first branch line (R1) is connected to the first fuel nozzle (601) and whose flow rate is controlled by a second flow rate adjusting valve (30), the second branch line (R2) is connected to the second fuel nozzle (602) and whose flow rate is controlled by a third flow rate adjustment valve (40), and the third branch line (R3) is connected to the third fuel nozzle (603) and whose flow rate is controlled by a fourth flow rate adjustment valve (50), wherein the fuel control method comprises: Determining an opening degree of the first flow rate adjusting valve (20) of the trunk / main fuel supply line (Ra) on the basis of a fuel control signal command value according to a power of the gas turbine (1), Determining the degree of opening of each of the second, third and fourth flow rate adjustment valves (30, 40, 50) and thus the respective fuel distribution ratios of the first fuel nozzle (601), the second fuel nozzle (602) and the third fuel nozzle (603) of the first, second and third branch lines (R1, R2, R3) on the basis of an operating situation of the gas turbine (1), Determining a correction value of the opening degree for each of the second, third and fourth flow rate adjustment valves (30, 40, 50) of the first, second and third branch lines (R1, R2, R3) on the basis of a value of a pressure difference between a fuel pressure upstream of each of the first, second and third fuel nozzles (601, 602, 603) and a corrected fuel pressure for the fuel pressure at an outlet of the first, second and third fuel nozzles (601, 602, 603), and Determining the correction value for the fourth flow rate adjustment valve (50) in a case where the pressure difference between the fuel pressure upstream of the second fuel nozzle (602) and the corrected fuel pressure for the fuel pressure at the outlet of the second fuel nozzle (602) is reduced to reduce the fuel distribution ratio of the third fuel nozzle (603). [7] A program for causing a computer to carry out the fuel control method according to claim 6.

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